I questioned somebody about this last time I traveled to Japan and at that time I was told that it is common for people that are sick to wear a mask to help prevent the spread of the germs. I was told it was more a courtesy to others than for the person wearing it. I'm sure there are exceptions and some might wear them to protect themselves.

I saw this quite a bit on my trips to Japan, and it makes sense to me. Yes, the face masks don't provide hospital-quality protection. But they do provide SOME protection, especially if you are the one who is sick. Then if you sneeze or cough, the germs stay mostly inside your mask and you don't spread them around so much. The whole thing makes more sense if you have ever seen how densely people live in large cities in Japan. On the subway, the cars are so full that white-gloved helpers on the platform will strongly push on the crowd of people to help force more of them onto the train. This way, more people get on the train without having to be personally rude and do the pushing themselves. Public toilets are often equipped with small devices that play a flushing noise at the press of a button which allows the occupant to cover up any embarassing noises without wasting water. Japanese people - and I know I'm generalizing here - walk a finely balanced line between personal privacy, public courtesy, and the pressures of living in such close quarters. Homes are smaller, cars are smaller, elevators are more crowded. People maintain less personal space, and there are many cultural coping mechanisms to make this more tolerable. I understood the masks to be a part of this. Wearing one shows that you are being careful to preserve hygeine. But a full-on face mask, like the nose-pinchy type, would be very uncomfortable to wear all day. The open masks are a compromise that maintains some effectiveness against the spread of germs while being comfortable enough to tolerate wearing all day.